1. Field of the Invention
The present invention relates to an integrated multi-measurement system for simultaneously measuring various physical properties, including thickness, electrical resistance, differential pressure and so on, with respect to compression, of a gas diffusion layer for a polymer electrolyte fuel cell.
2. Description of the Related Art
A fuel cell is a cell for directly converting chemical energy produced through oxidation of a fuel into electrical energy. A fuel cell, called a kind of power generator, is similar to a typical chemical cell in terms of the use of a redox reaction, etc. However, the fuel cell continuously receives reactants from the outside of the cell and continuously discharges reaction products to the outside of the cell, unlike the chemical cell where a cell reaction is performed in a closed system.
A variety of fuel cells using gaseous fuel including hydrogen and fossil fuel such as methane and natural gas and liquid fuel including methanol (methyl alcohol) and hydrazine have been devised. In particular, there are a low-temperature fuel cell which operates at a temperature of about 300° C. or lower and a high-temperature fuel cell which operates at a temperature above 300° C. Also, a high-temperature molten carbonate fuel cell for improving power generation efficiency without using a precious metal catalyst is referred to as a second generation fuel cell, and a solid electrolyte fuel cell exhibiting higher power generation efficiency is called a third generation fuel cell.
Examples of the fuel cell include a phosphoric acid fuel cell (PAFC), an alkaline fuel cell (AFC), a polymer electrolyte fuel cell (PEFC), a molten carbonate fuel cell (MCFC), and a solid oxide fuel cell (SOFC).
Among fuel cell examples, the fuel cell related to the prevent invention is a PEFC. As shown in FIG. 10, a conventional PEFC is configured such that a porous anode and a porous cathode are respectively attached to both sides of a polymer electrolyte membrane and a gas diffusion layer is then further attached thereto.
Specifically, the main components of the PEFC include a polymer electrolyte membrane, electrodes (anode, cathode), a gas diffusion layer, and a separator for a stack. As such, two electrodes including the anode and the cathode are attached to the polymer electrolyte membrane through hot pressing, thus forming a membrane-electrode assembly (MEA). The construction and performance of the MEA are important to the PEFC.
A fuel cell stack is formed by stacking tens to hundreds of single cells respectively responsible for an electrochemical reaction. The single cell or the stack thereof is configured such that both end plates are tied with a tie rod or pneumatic pressure in order to reduce contact resistance between the components. Each end plate includes a reactive gas outlet, a reactive gas inlet, a cooling water circulation line, and a connector for electrical power output.
FIG. 11 shows a PEFC stack made by Ballard. In addition to the stack, an actual system includes a fuel reformer, an air compressor, a heat/water treater, and a power converter.
The PEFC has advantages such as a high output density, a low operating temperature of 100° C. or less and high corrosion resistance of an electrolyte, and is also advantageous in terms of few limitations for a mounting place thereof, simplification of the equipment's structure, applicability to small-capacity equipment (having power of ones of kW), very safe operation repeatability (convenient operating safety), availability at room temperature and quick startup (for emergency and military power) Thus, the PEFC may be widely applied to various fields, including 250 kW industrial modules, tens of kW commercial applications, ones of kW residential applications, 80 kW automobiles, 150 kW buses, small fuel cells less than 1 kW, and subwatt IT products.
FIG. 12 is an exploded perspective view of the fuel cell of FIG. 10 or 11, in which a current collector is disposed at both ends of the fuel cell, an MEA is located at the center of the fuel cell, and a gas diffusion layer is disposed between the current collector and the MEA. Each current collector includes a separator, a gas inlet and a gas outlet.
In the single fuel cell, the gas diffusion layer plays a role as a pathway for transferring a reactive gas and water which is a product and performs thermal conduction and electrical conduction. Upon actual operation, because the gas diffusion layer is subjected to clamping pressure, there is a need to examine changes in physical properties occurring in the clamping state.
Also, because the effect of the degree of clamping pressure in the fuel cell on performance of the fuel cell is very great, optical clamping conditions must be found. Such optical clamping conditions may be found within optimal ranges of thickness, contact resistance and gas permeability with respect to compression.